Dietary Carbohydrates are NOT “Toxic” to Cats

Folks who are critical of commercial pet foods or advocates for raw diets and other alternatives often rail against the evils of carbohydrates. The idea that dietary carbs cause disease is a central thesis of the recent “Truth About Pet Cancer” video series (my response to which is coming soon!). With cats in particular, the claim is made that since they are obligate carnivores, carbohydrates are effectively poison for this species, causing diabetes, cancer and all sorts of other diseases. There’s only one small problem with this claim: it isn’t true!

What is true is that cats are obligate carnivores, meaning that they only eat animal prey in the wild. However, the idea that this means animal prey is all they can eat is a fallacy. Cats do have biological adaptations to eating prey, which means they have no requirement for carbohydrates in the diet, and they require more protein, and somewhat different amino acids in the diet than dogs and humans. However, this is a far cry from the wild claims made about carbohydrates causing disease.

At the recent American College of Veterinary Internal Medicine (ACVIM) forum, there was a great evidence-based presentation reviewing this subject:

Dr. Laflamme begins by referring to a 2010 ACVIM consensus statement which I reported on many years ago. Though no complete consensus was reached, the bottom line was that the most important dietary risk factor for cats, and the most common nutrition-related disorders (diabetes and obesity) are due primarily to excessive calorie intake, NOT dietary carbohydrate content.

Research has shown that cats can digest and utilize carbohydrates nearly as well as dogs, so they are an appropriate source of calories.1-4 Carbophobes often behave as if all carbohydrates are the same, and that any carbohydrate is equivalent to eating pure sugar. That is, of course, nonsense. While too much refined simple sugar in the diet can have negative effects on both humans and cats, complex carbohydrates and fiber do not, and can actually have positive effects. Dr. Laflamme points out that while it is possible to raise blood sugar in cats with extreme dietary manipulations (fasting them then feeding a single meal very high in carbs and low in protein), the normal type of carbohydrates used in cat foods fed in a normal manner has no apparent effect on glucose or insulin levels, so there is no reason to believe these diets would increase the risk of diabetes.

In a more real-world type of study, there have been three reports looking at what actual pet cats are fed and whether this influences the risk of diabetes. One of these found a greater chance of diabetes in cats fed only dry or only canned compared with a combination of the two.5 This makes little sense physiologically, and the study did not consider changes in diet that often go along with the diagnosis and treatment of diabetes, so this result is questionable. Two other similar studies which did look specifically at the diet fed before the onset of diabetes found no association between dry diets and diabetes.6-7 It is also worth noting that the vast majority of cats in the U.S. and Australia eat at least half dry food, and almost half of cats eat only dry. If dry food causes diabetes, a lot of cats should have this disease, yet this disease only occurs in between 0.2% and 0.75% of cats.

Another important health concern often blamed on carbs is obesity. Contrary to the claim that dietary carbohydrates cause obesity in cats, there is evidence that diets relatively higher in carbs than in fat actually reduce the risk of this problem. Cats naturally limit their own carbohydrate intake, and carbs are less caloric than fat, so cats on higher carb diets tend to eat fewer calories and so are less likely to be obese. Some of the low-carb dets marketed to reduce obesity and diabetes risk based on the idea that carbs are “bad” for cats actually raise the risk of obesity because they are high-fat and very caloric!8

Of course, anything can be harmful in excess, even water and oxygen. Extremely high carbohydrate diets, above about 50% of calories, can cause diarrhea and potentially raise blood sugar levels in cats. Such diets also make it difficult to ensure adequate protein intake. However, the existing evidence suggests that in appropriate forms and amounts, there is no reason to believe dietary carbohydrates are harmful to cats, and they even have some potential benefits. The fear-mongering about carbs and commercial diets promoted by advocates of raw food and alternative medicine simply isn’t consistent with the facts.

14 Responses to Dietary Carbohydrates are NOT “Toxic” to Cats

It has been shown that a dry food only diet, thus carb heavy, Is detrimental to a cats health. In fact, many vets strongly recommend going to a wet food only diet..now. How did this change come about?
I’m not a feed this way only pet owner. I believe variety is best, but I also try to limit as much as possible carbs in my cat’s diet. Obligated means must have, so cats must have meat protein without which they will sicken and die. Their systems are not designed to process carbs. We can feed carb heavy foods due to processing and supplements. Once upon a time, cats did die on kibble due to nutritional lacking. Science is a wonderful thing, but it is not always correct and “anecdotal” evidence is not always wrong. There are “screwups” on both sides.

Unfortunately, you have been misled. It has not been established that dry diets are harmful or that, if they are, the reason is the carbohydrate content. The entire point of this post and discussion is to raise awareness of the fact that these are unproven beliefs, not established facts, and that the existing evidence does not support such claims. Conclusions drawn from anecdotes can be true or false, but anecdotes themselves can’t prove them true or false since every claim is always supported by personal experiences, from the supposed dangers of dry cat food to the truth of astrology and the existence of aliens on Earth. You can always find stories for and against any claim, so stories themselves can’t prove claims true or false, which is what science is for.

The World Health Organization strongly advises people to avoid processed foods, namely due to their proven link with cancer (http://www.who.int/features/qa/cancer-red-meat/en/). However, most veterinarians promote processed foods as the best nutrition for pets. Why is it different?

Before you use the excuse “humans and pets are different”, let me tell you that I am not just a pet owner spending all my free time reading pet blogs written by untrustworthy and biased authors. I am a researcher with a PhD in Evolutionary Biology, so heads up: I might be a little harder to trick! If processed foods should be avoided by people, then processed foods should be avoided by pets. If you disagree, please elaborate why is there less risk for pets in comparison to humans, with some NCBI references.

Bottom line: if you were given two complete and balanced pet foods for the same price, but one was processed/dry and the other was freshly made, which one would you pick for your pet? (We both know the answer.)

The main problem with your reasoning is the concept of “processed.” Obviously, any food is “processed” if you don’t pick it out of the ground and eat it unwashed and uncooked. That’s obviously not a healthy choice. In human nutrition, “processed.” generally refers to convenience and snack foods, which are something entirely different in design and production than commercial pet foods. Here is a more detailed discussion copied from another of my articles:

“Processed” pet foods
I think it is also important to address the concept of “processed” food, since this term is egregiously misused in TAPC. Obviously, anything not eaten raw and unwashed is “processed” to some extent, the term is broad enough to be nearly meaningless. And despite the negative implications usually attached to the phrase, some kinds of processing clearly improve the safety and nutritional value of foods (washing and cooking, in particular). However, in TAPC, the term is used in an exclusively negative way, as a synonym for “unhealthy” and “toxic.”

Most people probably hear the term and think of snacks and convenience foods for humans – potato chips, packaged hot dogs, frozen chicken nuggets, and so on. And there is some limited evidence that such foods may increase cancer risk in humans. Whether this is simply an association (e.g. people eating such foods are more likely to be overweight, exercise less, and have other risk factors for cancer), or a causal relationship (something in these foods increase cancer risk, directly or indirectly through something like increasing obesity) is unclear. In any case, clearly no one thinks a diet of convenience foods and snacks alone is healthy, and mainstream dietary guidelines recommend plenty of fresh fruits and vegetables, whole grains, low-fat protein sources, and so on because there is evidence to support the health benefits of such a diet. Therefore, it is reasonable to wonder how a packaged commercial diet could be safe or healthy for our pets.

One key difference between human convenience foods and pet food is that the former are designed primarily to appeal to consumers. Taste, appearance, mouth feel, packaging, price, and most other characteristics of packaged foods for humans are aimed at getting people to buy them. Nutritional considerations are a negligible factor, apart from those that can be used as marketing tools (e.g. calling a cookie full of sugar “low-fat” or slapping a meaningless label like “no GMO” or “All Natural” on something to fool people into imagining it is healthier).

Pet foods, in contrast, are typically designed by nutritional experts to be complete and balanced, and support normal health. Sure, they have to be appealing to pets in terms of taste and smell, and to owners (which includes being affordable and often leads to plenty of meaningless verbiage on packages). However, extensive research evidence exists demonstrating the nutritional needs of companion animals, and meeting these needs is a core requirement for a pet food from a reliable manufacturer. Pet foods are intended to be the primary source of nutrition, and they are formulated and manufactured with this in mind.

Now most pet foods intended for adult maintenance or for growth in puppies and kittens have not been tested in large-scale, long-term clinical studies to demonstrate their impact on health. Some feeding trials are done for many diets, but these are foods, not medicines, so they are not required to meet that level of evidence. There are only a few commercial diets specifically intended for therapeutic medical uses, such as supporting animals with kidney disease, dissolving bladder stones, and so on. These have been through extensive pre-clinical and clinical trial testing to validate medical claims made for them.

While it would be nice to have this kind of data for all commercial diets, it is false to suggest this means the health effects of feeding commercial foods haven’t been studied. And it certainly makes no sense to suggest that alternatives, such as raw or homemade diets, are healthier when there is even less evidence for the impact of those diets. The limited evidence so far suggests these alternatives are likely to be nutritionally incomplete or unbalanced (e.g. 1, 2, 3, 4) and have risks, such as exposing humans and pets to serious infectious diseases, that are not outweighed by any proven benefits (1, 2, 3).

In theory, fresh, homemade diets that are properly formulated might be healthier than commercial pet foods. This is a reasonable hypothesis that can and should be investigated. However, the folks behind TAPC are basing their claims entirely on ideology, misuse of pre-clinical science, and ignoring the evidence and expertise of real veterinary nutrition experts, who are repeatedly dismissed using the shill gambit. The fearmongering in this series about “processed” foods and commercial pet diets is not founded on real evidence and is deeply misleading to pet owners trying to make decisions about how best to feed their animal companions.

“Q: What do you consider as processed meat?
A: Processed meat refers to meat that has been transformed through salting, curing, fermentation, smoking, or other processes to enhance flavour or improve preservation.”

Most commercial pet foods (especially kibble) fall entirely within this definition. It is food (mostly unfit for human consumption) that is highly transformed to enhance flavour and improve preservation. It’s a perfect fit to the definition of “processed” established by the WHO. Furthermore, it is almost always cooked at high temperatures, which may be linked to an even higher carcinogenic risk, as once again stated by the WHO. Quote:

“Q: Do methods of cooking meat change the risk?
A: High-temperature cooking methods generate compounds that may contribute to carcinogenic risk, but their role is not yet fully understood.”

Although the evidence may still be limited, it was enough for the WHO to consider processed foods carcinogenic to humans. Quote:

“Q: Processed meat was classified as Group 1, carcinogenic to humans. What does this mean?
A: This category is used when there is sufficient evidence of carcinogenicity in humans. In other words, there is convincing evidence that the agent causes cancer. The evaluation is usually based on epidemiological studies showing the development of cancer in exposed humans. In the case of processed meat, this classification is based on sufficient evidence from epidemiological studies that eating processed meat causes colorectal cancer.”

And this decision of the WHO to include processed meats in the Group 1 (carcinogenic) was due to a suspicion of a causal link (and not just an association). Quote:

“Q: What makes red meat and processed meat increase the risk of cancer?
A: Meat consists of multiple components, such as haem iron. Meat can also contain chemicals that form during meat processing or cooking. For instance, carcinogenic chemicals that form during meat processing include N-nitroso compounds and polycyclic aromatic hydrocarbons. Cooking of red meat or processed meat also produces heterocyclic aromatic amines as well as other chemicals including polycyclic aromatic hydrocarbons, which are also found in other foods and in air pollution. Some of these chemicals are known or suspected carcinogens, but despite this knowledge it is not yet fully understood how cancer risk is increased by red meat or processed meat.”

So, after all these statements by the WHO, how can you still say something like this: “While it would be nice to have this kind of data for all commercial diets, it is false to suggest this means the health effects of feeding commercial foods haven’t been studied. And it certainly makes no sense to suggest that alternatives, such as raw or homemade diets, are healthier when there is even less evidence for the impact of those diets.”

When a vet recommends a processed pet food over fresh diets as ideal/optimal nutrition for a dog or a cat, he/she is doing the exact opposite to all the recommendations made by the World Health Organization for humans. The exact opposite. And my question is simple: why?

You fail to mention that the WHO information you cite refers exclusively to foods intended for human consumption, and to the methods by which they are “processed.” There is no mention of commercial pet foods or the methods of manufacturing these because, as I keep pointing out, the WHO definition is not intended to apply to those and these methods are quite different. “Salting, curing, fermenting, smoking” are methods not used in the production of pet foods.

You also cherry pick your evidence. There is concern about potentially carcinogenic compounds formed whenever meat is cooked. However, the reason we still cook our meat is that the evidence also shows much greater risk, from infectious disease and parasitism, if meat is eaten raw, which you ignore here. The WHO is certainly not recommending eating raw meat. You left out the part of the document addressing this point:
“Is eating raw meat safer?
There were no data to address this question in relation to cancer risk. However, the separate question of risk of infection from consumption of raw meat needs to be kept in mind.”

You also ignore the differences among processing methods. Risk if much greater, for example, with salted and smoked and fried meat than with other kinds of processing, and none of these methods are used in making commercial pet foods.

Finally, the theory that heterocylclic amines produced in heating meat cause cancer is based on lab studies, not on actual studies of dogs and cats eating commercial foods. As your own quote points out, these “may” cause cancer, but “their role is not fully understood.” Yet you jump right to the conclusion that commercial diets raise cancer risk based on this theory, in the absence of any epidemiologic evidence that is actually true. Show me a study comparing cancer rates in matched animals (species, breed, age, other risk factors) eating commercial and some specific alternative diet, and if the evidence shows lower risk, I’ll change my mind. But at this point, you’re argument is based on unproven theories and unrelated evidence relevant to methods of processing food for human consumption that don’t apply to the production of pet foods.

“When a vet recommends a processed pet food over fresh diets as ideal/optimal nutrition for a dog or a cat, he/she is doing the exact opposite to all the recommendations made by the World Health Organization FOR HUMANS.”

Obviously, there is no mention of commercial pet food in the WHO website because people do not eat commercial pet food nor there is something like “people kibble” out there. (Strangely, since kibble is so great! Some entrepreneur should pick this brilliant idea.)

Indeed, the WHO refers four EXAMPLES of processing methods (“salting, curing, fermenting, smoking”), but you “failed to mention” what followed those examples, in the same sentence: “, or other processes to enhance flavour or improve preservation”. So, who is cherry picking after all? Obviously, they wouldn’t list all processing methods, and most commercial pet foods undergo processes to enhance flavour and improve preservation (e.g. they are packed with additives and preservatives). Here is the PetMD description of the process of making kibble (https://www.petmd.com/dog/nutrition/evr_multi_dry_pet_food):

“In modern times, the process of creating dry pet food is done by either baking or extruding. Originally created to produce puffed breakfast cereals, the machines that are used for the extrusion process are an efficient method for manufacturing large quantities of nutritious, shelf-stable pet foods. This process begins with the dough — a mixture of raw dry and wet ingredients that are mixed together until they form a dough-like consistency. This dough is then fed into a machine called an expander, which uses pressurized steam or hot water to cook the ingredients. While inside the expander, the material is under extreme pressure and high temperatures. The dough is then forced — or extruded — through specially sized and shaped holes (called die), where it is cut off by a knife. This process must be done while the dough is still compacted from the high pressure, since once the dough pieces have lost the effects of the high pressure, they puff up. The puffed dough pieces are then passed through a dryer so that any remaining moisture is drawn out. The dough has now been transformed into kibble, which is sprayed with fats, oils, minerals and vitamins and sealed in packages before the fats and oils can spoil.”

If you insist that, after all theses processes, commercial pet food is not a highly processed food, then we will have to agree to disagree, because it seems that you are just manipulating the argument to make a point.

I admit I may have accidentally mislead you into thinking that I’m a raw food advocate. I’m not. I have one dog and three cats, and I don’t feed them raw food, never did and probably never will. But from raw to “extreme pressure and high temperatures” there are a myriad of intermediate cooking methods, which would avoid the risks of both raw and highly processed foods. So, please, lets avoid fallacies like that false dichotomy you just used.

Finally, you ask me for scientific papers comparing commercial pet foods to alternative diets, but I’m assuming you already have those, or else you wouldn’t be such an advocate of commercial pet foods over fresh diets. Can you please give me those references? Actually, I asked for them in my first comment here, but with no success.

Limited evidence or theories based on a scientific background should be enough to, at least, a “better safe than sorry” approach. This is my humble opinion and apparently the humble opinion of the WHO, which included human processed foods in Group I (carcinogenic), based also only on limited evidence and theory. And, honestly, I don’t understand what’s the problem on following a “better safe than sorry” approach when the alternative is so easy to accomplish. I really don’t get it.

As a final note, I would like to say that, contrary to what you might be thinking, I’m not against what you are doing here on your website. I’m really not. I like your blog, and that is why I follow your posts. Go ahead and expose those false claims like homeopathy. That’s great and important! I just disagree with your approach regarding nutrition.

Again, you’re missing my point. The WHO statement does not apply to pet foods, so bringing it up as a way of suggesting there are health risks associated with pet foods is misleading. The specific methods of processing I quoted don’t apply because they aren’t used (salting, etc.). As for “other methods,” that’s pretty vague, so it’s hard to know whether or not this includes extrusion or cooking or adding salt or other flavorings, or other methods not specifically mentioned. Anything you do to food likely enhances its flavor and palatability, so again, unless you’re advocating eating raw, unwashed, unseasoned food, anything you eat or feed your pets is going to be processed by this definition. Does this mean everything we eat is carcinogenic?

The key is that if you are going to claim fresh food is healthier than commercial food or that commercial dog food raises disease risk, it’s up to you to provide the evidence to support this claim. All I am claiming is that there is no evidence this is true, and until someone produces some you are just speculating. This doesn’t make me an “advocate” for commercial diets, merely a critic of the alternatives that are often lauded as better without real evidence to support such a claim.

The conflation of potato chips and hot dogs with commercial pet foods as both “processed” is disingenuous and misleading as well. The hypothesis that fresh food may have health benefits compared to kibble is a reasonable one, and it may someday prove to be true. However, right now, you are taking it as fact when it is merely a possibility, and you are ignoring all the evidence that cats and dogs can live long, healthy lives on current commercial diets. The precautionary approach, which you seem to suggest, would be to stick with diets that have proven very effective and are formulated based on extensive research in cats and dogs rather than to encourage people to seek alternatives (which often will be unbalanced homemade diets, raw diets, and others with clear risks) when there is not yet evidence that these are as good or better than extant options.

After all this discussion, I just came to the conclusion that, actually, we do not think that differently about this subject. I finally read something like this coming from you, which eased my discomfort: “The hypothesis that fresh food may have health benefits compared to kibble is a reasonable one, and it may someday prove to be true.”. After all your reasoning comment after comment, I thought you didn’t find that hypothesis reasonable. So, basically, we just have different approaches towards that reasonability: while you prefer to wait until there’s solid evidence and targeted studies (which may take decades to come, i.e. more than the entire life of our pets), I think it is worth to start right now. And I think this way because I don’t feel comfortable in ignoring that very reasonable hypothesis, because, at the end, when those studies come, there are only two possible scenarios:

a) fresh diets and commercial pet foods are equally healthy, so I didn’t harm my pets in any way, I just had a lot of unnecessary work preparing their meals;

b) fresh diets are healthier than commercial pet foods, so I made a good decision.

Overall, fresh diets score better when averaging both scenarios. And, yes, I excluded that third scenario deliberately (fresh diets being worse than commercial pet foods). I excluded it because I can’t think of a reason why this would be true, if those fresh diets are complete, balanced and formulated by a certified veterinarian/nutritionist. But I admit I may be missing something.

However, I’ll have to add some additional comments to some of your comments:

a) “However, right now, you are taking it as fact when it is merely a possibility, and you are ignoring all the evidence that cats and dogs can live long, healthy lives on current commercial diets.”

As a researcher, this argument is not valid to me. Smoking causes cancer, but, however, countless smokers die of old age.

b) “The precautionary approach, which you seem to suggest, would be to stick with diets that have proven very effective and are formulated based on extensive research in cats and dogs rather than to encourage people to seek alternatives (which often will be unbalanced homemade diets, raw diets, and others with clear risks) when there is not yet evidence that these are as good or better than extant options.”

You make it sound like it is impossible and/or nightmarish to make a complete and balanced homemade pet food, with ingredients fit for human consumption that you can buy in any supermarket. What about veterinarians (which certainly have a solid academic basis on nutrition) helping to formulate those recipes to their patients? After all, that’s what people do when they want to make better decisions on nutrition: they go see a nutritionist, and the nutritionist tells them what to eat. The idea that a pet not eating commercial pet food will most probably have health issues due to nutrient imbalances and/or deficiencies is, per se, fearmongering, the very concept you try so hard to fight here on your website. And it is also a very naive belief, if taken into account that most commercial pet foods may not be that complete and balanced after all (https://www.nature.com/articles/s41598-017-17159-7). People also have daily nutrient requirements and yet we do not need to eat food from a bag saying “complete and balanced” to thrive.

Miguel Morgado Santos, you left out the possibility that home-made food is worse for pets than kibble, there are three possible scenarios. However if you do seek the advice of a nutritionist for the species you are making food for you should increase your chances that your home-made food is at least equal to kibble significantly. At least I do expect kibble producers do have a at least one nutritionist on staff, if not I’d stay away from that brand.

I do not think that you can assume that humans would not do better on a regulated diet formulated for humans. Left to themselves humans do not go for healthy food, a giant diet industry which is running after every new fad, the existence of plenty of very successful fast food chains and thousands of books on the subject should be evidence for this. If you add in recreational drug choices it doesn’t get any better. Making healthy food choices as a human is a learned behavior, which means you acquire a lot of knowledge during your life if you achieve it.
Actually most pet owners probably make a lot better food choices for their pets than for themselves. I know I do.

Since you can’t say it, I will. Most of the fear mongering about carbs is coming from Dr. Lisa Pierson and her disciples. There’s an entire forum full of people who will attack anyone who suggests they might be giving their kitty anything but the highest-priced wet food, citing “Dr. Lisa,” as if she’s Jesus Christ.

While it may be necessary to adjust a sick or overweight cat’s diet, Pierson’s fanaticism is a bit much. Purina and Hill’s both have veterinary nutritionists on staff who provide in-depth, accessible information for consumers. I’m sticking with science over scare tactics.

Ok, carbohydrates are not toxic to pets. But are they necessary? I ask this because there are no minimum requirement for carbohydrates in AAFCO, FEDIAF or NRC, contrary to both other macronutrients (protein and fat).

As far as we can tell, cats and dogs have no absolute requirement for carbohydrates. In theory, they should be able to survive on a pure fat/protein diet. We know they can both utilize carbs effectively as an energy source. There are also some suggestions, especially in dogs, that certain carbohydrates, particularly fiber or various types, can have health benefits in terms of supporting a healthy intestinal microbiome, regulating GI motility, regulating blood glucose levels, and so on. Interestingly, there is also some evidence that cats actively prefer foods with higher carbohydrate content, though not all studies find this. So while it is unlikely that a very low or zero carb diet would be seriously harmful to dogs or cats, it is unclear whether it would have any beneficial effects, and it is possible, especially in dogs, that some kinds of carbs may be beneficial.